Rubber compositions and preparation thereof



V "2.554.126 RUBBER COMPOSITIONS AND PREPARATION TnEREoE V that the subject compounds are sometimes assigned structures other than that set forth herein. It vw'll be under Robert E, Miller, Dayton, Ohio, 'assign'or to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware No Drawing. Filed Dec. 23, 1957, Ser. No. 704,327 8 Claims. or. 260-453) The present invention is directed to a method of retarding or preventing the deterioration of rubber due to aging or exposure to the atmosphere which involves treating rubber with furoxans. The invention is further directed to rubbers-both natural and synthetichaving furoxans incorporated therein. An object of the present invention is to provide chemicals for retarding the deterioration of rubber and rubber like materials which tend, to deteriorate due to action of oxygen orozone in the air. A further object is to provide chemicals which additionallyfactjto improve the resistance of rubber to cracking or tearing when subjected to strain or flexing under atmospheric conditions. A further object is to provide a new class of rubber antidegradants. I The antioxidants or antidegradants utilized inthe present invention can be represented by the formula:

stood that the antidegradant activity of the subject compounds is contemplated as within the present invention regardless of how they are name'd of structurally illus tratcd. I I

The furoxans for use in the present invention can be prepared by known procedures, e.g., by oxidizing dioxime compounds to obtain the furoxan structure' Suitable me of p p i s dia kylr 9r al w 'arylefuroxalis, e.g., are described by R. Scholl, Berichte, 23, 3490-3505 (1890). An excellent procedure for the preparation of diphenylfuroxan is set forth in the example below.

,EXAMPLE 7 Benzaldoxime, 61 grams 0.5 mole) was dissolved in 200 cc. absolute ether and cooled to 3 C. by means of an ice bath. A 92-gram (1 mole) portion of N 0 was added dropwise during a 1-hour period at a temperature mixture was then treated with 200 cc. of 10% aqueous potassium carbonate solution. The ether solution was decanted and shaken with 1 liter of 10% potassium carwhich R and R can be selected from the group consisting of hydrogen; aryl radicals, such as phenyl and substituted phenyl radicals, e.g., phenyl, o-tolylp-ethylphenyl, m-isopropylphenyl, o-hydroxylphenyl, nitrophenyl, p-chlorophenyl, etc., and polycyclic aromatics such, as p y anthracyl, a iphatisj rq a flfiq e f those resulting from combinations of the aryl and alkyl.

groups given by way of example above, e.g., [rt-phenylethyl. As the cyclic furoxan structure is responsible for the antidegradant activity, the actual compositionof the ,R and R groups is not too important, although furoxans with some'R and R groups will have a higher degree of activity than furoxans with other such groups.

examples of furoxans, all having suitable antidegradant activity, are diphenylfuroxan, 3-p-ethylphenyl-4-phenylfuroxan, di-o-hexylphenylfuroxah, vdi-mhexylfuroxan, dinaphthylfuroxan', di-cyclohexylfuroxan, di-or-thienylfuroxan, di-a-furylfuroxan, 3-p-methoxypheny1-4-rnethylfuroxan, phenylfuroxan, furoxan, etc.

It will be realized that the furoxan compoundsutilized herein are sometimes designated as 2,3 -epoxy-2,3-dihydrofurazans, furazan-2-oxides,for glyoxime peroxides, and

Some

.bonate" until no further color was observed in the alkaline washings." The ether solution was separated and the ether was evaporated, leaving 'diphenylfuroxan as a yellow solid along with a small amounto f'red oil; the 24.8 grams of. diphenylfuroxan, having a melting point of ll4+118 0., represented a conversion of 41.8%. An

additional amount of 'diphenylfuroxan was isolated from the alkaline wash liquors. v v

The above procedure is readily applicable to the preparation of other diarylfuroxans. The diarylfuroxans, in general, are suitable for use in rubber formulations as described herein; thediarylfuroxans in which the aryl groups are monocyolic are especially suitable for such use.

The following evaluations and the procedures and compositions employed therein are illustrative of the invention, but the inven-tion isnot limited thereto. f As representative 'rubberjforn'llilations for the evaluation of the antidegradant properties of furoxans, the following formulations were prepared, all parts being by weight. 1

VAB,CD

Smoked Sheets -r. .4... 100 100 Carbon Black... 50 50 ocuHoacocn \IM or NQrONnPO or wmomwo As the carbon black in these formulations, the trademarked product, Philblack 0 was employed; the plasticizer was an asphalt-i0 materialParaflux. As accelerator, N-

(other molar ratios, e.g., 60 to/10 to 40 or'the like,

can be employed); Sulfaan-R is the proprietary name if for a vulcanizing agent (4, 4'-dithiomorpholine).

. Stock'A is a conventional natural rubber formulation and Stocks C and D are conventional GR-S formulations,

. pate ted Mar- 7, 9

3 4 Stock B is a Sulfasan-R formulation designed to pick up Table IV sulfur-sensitive materials. In evaluating the antidegra- TEMPERATURE RISE (AT) IN DEGREES OENTIGRADE dants, both the furoxan and the controls were employed in an amount of 1.5 parts by weight in the foregoing Formulation formulations. 5 Antldegradant The data in the following table demonstrates the anti- A B D ozone activity of diphenylfuroxan as compared to two commercial antidegradants. In the relative ozone ratings, Commercial 1 17, 5 30 Commercial I was taken as 100. gcr u grgg 1g g menymphenyb 10. 0

T bl I 3119 (liamlne 19.0

Diphenyliuroxan 16.5 14.6 23 OZONE RATINGS The results clearly indicate there is less heat build-up Anfldegmdant Formulation occurring in rubber formulations stabilized by diphenyll5 furoxan than in formulations stabilized by the other A B O antidegradants; the diphenylfuroxan stabilized rubber should, therefore, be more resistant to aging in use. 83333 53} is 22 100 The anti-outgrowth effect of furoxans is shown by data Dlp e y 107 110 112 in the following table in which the flexes to failure of g cured samples having a slight out are indicated in kilo- It is thus demonstrated that diphenylfuroxan is not only cycles; the measurements were made on an India flexing equivalent to these commercially accepted antidegradants machine at 100 C. iifiilgtOZOflC activity, but is, in fact, superior in such Table V The antioxidant activity of diphenylfuroxan was then 25 CUTGROWTH RESISTANCE IN KILOGYCLES compared to that of a commercial antidegradant in a molded butadiene-styrene rubber (formulation C) by Anfldegmdam Fmmulamn aging in an air oven for 72 hours at 100 C. The results are reported as percentages of retention of the modulus A B D of elasticity.

P rcent fi i i i iT 50 Commercial I e 135 Ngyllglld i gi t rgsg-N-cyclohexyl- N -phenyl'p-phen- 625 Diphenylfuroxan 135 Dlpheflylfllmxim 600 550 50 iiz g i $5 1 23; ggggg fggg s g gg s to an The data indicate that dighenylfuroxan is super or to anti- Thfi antiscorch activity of the fumxans is demom outgrowth activity to t e accepted commercial antidestrated by the data in Table II in which the time rei quired to scorch the cured formulations in a Mooney e.fur0XaI}-St.ab1hZed rubbers have gopd physmil s 135e Cis recorded. 40 properties, as indicated by the values obtained for d1- phenylfuroxan-stabilized rubbers which had been cured Table II at 144 C. for minutes, as recorded in Table VI.

SCOROH TIME IN MINUTES Table VI Formulation PHYSICAL PROPERTIES Antidegradant 45 A B O Formulation Mi ti ius s t r n g t ii giiiiiig (lbs.) (lbs.lsq.ln.) gommercial h 1&1). g 23. 8 niiiineiitimm 1136 a i::::::::::::::::::::::::::::::::: 2:222 2:332 iii D 1,925 3,360 490 It is apparent that diphenylfuroxan has very good antiscorch activity, the activity in the GR-S formulation The furoxans will ordinarily be employed in small being particularly notable. amount in the rubber formulations, e.g., about 0.5 part The resistance to aging of furoxan-treated rubbers is to about 3 parts per parts rubber, the parts being by further shown by Goodrich Flexometer tests at C., weight; but other amounts can. suitably be employed, in which the decrease in size and heat build-up of a lsuch as amounts up to 10% or more by Weight of the inch cured sample are measured after flexing at 1800 rubber in the formulation. The rubber formulation can cycles per minute; the results are recorded in Tables also contain plasticizers, vulcanizers, accelerators, curing III and IV below. 60 agents, stabilizers, carbon black or light-colored fillers,

Table 111 etc. AGOMPRESSION mg The furoxans can be incorporated into the rubber by various treatments, such as milling, kneading, mixing, Fmmulation masticating, calendering, and the like; or by addition to Antidegradant s5 rubber solutions or disperisons, or by addition to rubber A B 0 latex before its coagulation. The furoxans can be in corporated before, after, or at the same time as the other gommeruia} components of the rubber formulation.

P ll i y The rubber formulations containing furoxans can be f: g, (196' 70 suitably cured by conventional curingoperations; such as,

Diphenylturoxmi 0. 652

It is apparent that the rubbers containing diphenylfuroxan have greater dimensional stability than doQthe formulations containing other antidegradants.

for example, treatment at 30 pounds per square inch steam pressure for up to one or even two hours. Curing temperatures of C. to i 6. for 30 to 60 minutes are often suitable, e.g., at 144 C. for about 45 minutes. The

' 75 present invention is considered to include, taken sepanately or together, the steps of preparing rubber formulations containing furoxans and curing such formulations.

The term rubber as employed herein includes sulfur vulcanizable plastic material which possesses high extensibility under load coupled with the property of forcibly retracting to approximately its original size and shape after the load is removed. Examples of such materials are India rubber, reclaimed rubber, balata, gutta percha, copolymers of butadiene and styrene, butadiene and acrylonitrile, and butadiene and isobutylene, polybutadiene, chloroprene, and other natural or synthetically prepared vulcanizable products, particularly butalastics or those formed in major part from polymerizable diolefins; and other such materials which deteriorate upon aging.

The rubber compositions disclosed herein have valuable utility in the normal uses for which rubber is employed, such as in vehicle tires, conveyor belts, shock absorbers, coating materials, and the like, and have advantages in that they are resistant to aging.

What is claimed is:

1. The vulcanized rubber product obtained by vulcanizing a conjugated d-iolefin rubber composition containing diphenylfuroxan in an amount from 0.5 to 3 parts for each 100 parts of said rubber, the parts being by weight.

2. A composition comprising a copolyrner of butadiene and styrene and a small amount of diphenylfiuroxan as an antidegradant, the amount of diphenylfuro-Xan being from being by weight.

3. The composition of claim 2 in which the butadiene and styrene are in molar proportions of about to parts butadiene to about 10 to 40 parts styrene.

4. A composition comprising natural rubber and a small amount of diphenylfuroxan as an antidegradant, the amount of diphenylfuroxan being from 0.5 to 3 pants for parts of said rubber, all parts being by weight.

5. A rubber composition comprising sulfur vulcanizable conjugated diolefin rubber and 0.5 to 3 parts of diphenylfuroxan for 100 parts of said rubber, all parts being by weight.

6. A sulfur vulcanizable conjugated diolefin rubber containing 0.5 to 3 parts of diarylfuroxan for 100 parts of said rubber, all parts being by weight.

7. A sulfur vulcanizable conjugated d'iolefin rubber containing 0.5 to 3 parts or di-u-furyl furoxan for 100 parts of said rubber, all parts being by weight.

8. A sulfur vulcanizable conjugated diolefiu rubber containing 0.5 to 3 parts of di-a-thienylfuroxan for 100 parts of rubber, all parts being by weight. 

1. THE VULCANIZED RUBBER PRODUCT OBTAINED BY VULCANIZING A CONJUGATED DIOLEFIN RUBBER COMPOSITION CONTAINING DIPHENYLFUROXAN IN AN AMOUNT FROM 0.5 TO 3 PARTS FOR EACH 100 PARTS OF SAID RUBBER, THE PARTS BEING BY WEIGHT. 